Heat-treatment of metals



United States Patent 3,117,042 HE.- T-TREATMENT 0F fv/ETALS HeinrichBleehner, .lauresgasse 1/ 12a, Vienna iii, Austria No Drawing. Filedfan. 2, i953, Ser. N 706,557 Claims priority, application Austria Jan.4, 1957 1 Claim. (ill. 143-452) This invention relates to the productionof heat-treated workpieces of metal, particularly of steel.

It is an object of the invention to provide a method of heat-treatingworkpieces of steel to produce a substantially austenitic structure atroom temperature.

It is another object of the invention to provide a hardened,fine-grained steel structure which is superior in hardness, wearresistance, elasticity, and resistance to corrosion to martensitic andhardenitic structures of the same composition.

It is a further object of the invention to provide an improved method ofheat-treating workpieces by contacting them with a tool moved relativeto the workpiece.

It is a further object of the invention to provide an improved method ofshaping metal workpieces with a tool whereby the costs of tools and thecosts of tool trueing are substantially reduced compared to shapingtreatments carried out according to conventional practice.

It is a further object of the invention to provide a method of treatingmetal workpieces with a tool and simultaneously trueing the tool.

It is a further object of the invention to provide a method ofsurface-finishing metal workpieces which enables the production of ahigh finished at a fraction of the cost involved in a conventionalmethods.

It is a further object of the invention to provide an improved method ofhardening and surface-finishing workpieces of steel in one operation.

It is a further object of the invention to provide an improved method ofhardening and shaping workpieces of steel in one operation.

It is a further object of the invention to provide an improved method ofshaping and surface-finishing work pieces of metal in one operation.

It is a further object of the invention to provide an improved method ofshaping, hardening and surface-finishing workpieces of steel in oneoperation.

It is a furhter object of the invention to provide an improved method ofprofiling workpieces of metal, which can be combined in a singleoperation with surface-finishing and, in the case of workpieces ofsteel, with hardening and/ or surface finishing.

It is a further object of the invention to provide an improved method ofwelding metal workpieces.

Additional objects and advantages of the invention will become apparentas the specification proceeds.

According to one aspect of the invention, heat-treated workpieces ofsteel are produced by successively subjecting fractional portions of theworkpiece to a temperature rise above its critical range and causingeach of said portions immediately after it has been subjected to saidtemperature rise to cool below the martensite line at a ratesufiiciently high to retain a substantially austenitic structure.

A preferred mode of carrying out this method is offered by a method ofproducing heat-treated workpieces of metal, which comprises successivelycontacting frac-v tional surface portions of the workpiece wtih a toolmember at a pressure and relative speed sufficient to subject each ofsaid portions while thus contacted to a temperature rise above thecritical range in the case of workpieces of steel or above the meltingpoint in the case of workpieces of a metal other than steel, and causingeach of said portions of the workpiece immediately after it has thus3,11 1%? Patented Jan. 7, 1964 "ice been contacted to cool substantiallyto room temperature.

In this specification, the term fractional surface portion defines asurface portion which can be subjected to a temperature rise above thecritical range in the case of workpieces of steel or above the meltingpoint in the case of workpieces of a metal other than steel and whichdue to its small size will immediately return to the temperature of therest of the workpiece and of the ambient atmosphere, even if the sameare substantially at room tem- 0 perature, as soon as said portion is nolonger subjected to the conditions which caused said temperature rise.In connection with the production of the fine-grained hardened steelstructure mentioned hereinbefore, the term fractional surface portiondefines a surface portion which can be subjected to a temperature riseabove the critical range of steel and which due to its small size willbe cooled to a temperature below the martensite line at a ratesufficiently high to retain a substantially austenitic structure, by adissipation of heat to the remainder of the workpiece and to the ambientatmosphere, which are maintained substantially at room temperature, whensaid portion is no longer subjected to the conditions which caused saidtemperature rise.

In this specification and the appended claim, the term steel is used todescribe a metal which shows a behavior similar to steel when subjectedto a hardening and tempering treatment as is usual for steel.

It is usual to machine or work workpieces with vari ous tools. Tools areknown which are used for dividing or cutting only by virtue of theirhigh cutting speed. This gives rise to irregular hard portions at thecut surfaces and it is necessary to remove these hard portions beforethe subsequent processing of the workpiece. In order to increase thewear resistance of the usual workpieces a surface treatment is adopted.All these operations require a great expenditure of labor, time andenergy. The results, particularly those achieved in heattreatingrelatively small workpieces, are often fairly irregular. For this reasonit has been attempted to effect the heat treatment of the workpiecesmore quickly and more uniformly in automatic hardening plants, which maybe gas-fired or high frequencyor resistance-heated or the like and towhich the workpieces are fed immediately after the mechanical treatment.In all these methods of hardening, the quenching treatment gives rise todangerous internal stresses, which must be removed by a so-calledtempering treatment.

It has been found that when steel is first heated con siderably abovethe upper limit of the critical range, preferably to or above the fusionpoint, by a supply of energy in any desired form, and is then subcooledat the highest rate, the austenite, which in other cases is stable onlyat elevated temperatures, can be retained in a stable form in largequantities (e.g., up to 98%) even at room temperature. This is followedby a mechanical or other influence, particularly by a shock actioncaused by shaking, impact, machining or by the use of the workpieceitself, or by temperature, electrical or other influences, whereby asudden conversion in structure is caused which provides a structurewhich is superior to the previously known martensitic or hardeniticstructures by a much higher hardness, higher wear resistance, higherelasticity and resistance to corrosion, improved surface finish andother properties. This structure has only low internal stresses evenwithout additional heat-treatment. For this reason it does not split orcrack, remains firmly bonded to the underlying material and retains itsbrightness. By this method, carbon and alloy steels are given thedesirable properties of austenitic steels. The method is applicable withextreme ease due to the simplicity of the procedure and of the toolsrequired.

For instance, the use of a tool which has been treated by the method ofthe invention will be sufficient to initiate the hardening processimmediately, whereby the tool is given an extremely high hardness. Theintense, brief temperature rise and the quick cooling produced by themethod according to the invention do not give rise to stresses in thetool and workpiece. The resulting surface layer has a uniformsmoothness, is free of cracks, has no tendency to scale, remains bright,is resistant to corrosion and can be controlled in its thickness. On theother hand, the thickness of the layer and its depth of roughness remainconstant under constant operating conditions. In conection therewith thecore of the material to be hardened according to the invention may besubjected to any desired heat treatment. For instance, a core ofparticularly high elasticity may be provided with a surface layer ofparticularly high hardness and wear resistance, which surface layer isfirmly bonded to the core and does not peel off or detach. The energyrequired for intense heat ing and high-speed cooling may be produced bymechanical treatment without involving an expenditure of additionalenergy for this purpose. It is sufficient to increase the speed of thetool to produce a relative speed of at least 80 meters per secondbetween the workpiece and the tool at the point of contact. This speedis limited particularly by the need to ensure the safety of theoperator. The method of the invention has been carried out in practicewith relative speeds up to 260 meters per second between the workpieceand the tool. The working conditions such as the working pressurebetween the tool and the workpiece, the time of treatment of theworkpiece, the initial hardness or artificial hardness of the workpiece,its carbon content, its content of alloying constituents, the nature ofthe material, the feed rate, and the exact adjustment and/ or matchingof these conditions are of special importance in view of the very highrela tive speed between tool and workpiece. For this reason it isessential that the devices for adjusting and matching the variousworking conditions are constructed for perfect rigidity and freedom ofshake and that their coaction can be adjusted most precisely and can bemaintained constant. When all these requirements are fulfilled, highestqualities can be achieved, which were previously attained only with veryhigh expenditure.

Another factor which can be varied is the feed movement of the tooland/or workpiece. These movements may take place in differentdirections. The tool and/or the workpiece may be caused to reciprocate,oscillate, roll, e.g., on a surface, revolve on an arm, etc.

The tool used may consist for these high relative speeds of a roundmember, formed simply on the lathe, particu larly as a disc, and has aservice life which is a multiple of the service lives of previouslyusual tools. The expenditure of energy, time, labor and supervision areminimized.

Whereas a thin disc about 100 mm. in diameter and having an edgebevelled at an angle of about 45 has proved most satisfactory incarrying out the method of the invention, it may be replaced by a greatvariety of other tool member such as plain or profiled members in theform of discs, rolls, cones, or balls.

The extremely high ultimate tensile stress of tools of steel enablesspeeds which would cause immediate fracture of the urual ceramic orother grinding wheels.

The method of the invention may be adopted to perform shaping treatmentssimilar in eifect to milling, reaming, profiling, spinning, drawing,trueing, as well as for surface-finishing treatments similar and in manycases superior in effect, e.g., to grinding, press-polishing, honing andlapping. Surface-finishing treatments may be combined with shapingtreatments. When performed on workpieces of steel, these shaping and/ orsurface-finishing treatments can be combined with the hardening of theworkpiece. For instance, surface layers having a highfinishing andextremely high hardness may be produced on cutting parts of knives,surgical instruments and the like, on toothed wheels, bevel wheels, spurgears. worm wheels and spiral gears and on the points of needles and ofshafts. Profiling operations which can be performed by the method of theinvention include, e.g., the cutting of teeth on saws, wheels, thecutting of threads on screws, the forming of flutes on twist drills. Themethod enables even the profiling of very small precision parts such asfor watches. These parts may be cut from solid stock, hardened andfinished in a single operation.

The tool may contact the workpiece with a profiled portion in adirection at right angles to the axis of rotation of the tool or with asurface which extends parallel or at right angles or at any other angleto the axis of rotation of the tool.

For profiling operations, guides for the feed movement of the tool and/or workpiece may be employed.

The maintenance of the tools used in the method of the invention ispanticularly simple and inexpensive. It is sufficient to true them byhand or semior fully automatically by a hardened and tempered smoothsteel rod held against the tool. This true-ing can be controlled tosmoothen, temper, grind and/or polish the tool and provide it with anextremely hard layer. The trueing operation may be performedcontinuously or periodically while the tool itself is in operation.Tools having polished surfaces can be used to produce on the work-piecea particularly thin hardened layer (0.001 mm. or less) having aparticularly high surface finish.

Tools which are stationary in operation may be periodically trued bytreating them for a short time according to the method of the inventionwith a tracing tool rotating at high speed. In this way the tools can beprovided with particularly nicely ground, extremely sharp cutting edgesand extremely hard points. These edges and points have a very longservice life.

As a result, stocking problems are simplified and the tool account isreduced. Above all, the use of extremely for any subsequent heattreatment such as quench-hardening and tempering. The machines in whichsuch tools are used at high and very high relative speeds with respectto the workpiece are inexpensive in construction and simple inattendance. They are particularly suitable for full automation. Surfacesor hardened structures produced by such tools are smooth, can be givenparticularly high degrees of hardness, have a particularly highresistance to wear and resistance to corrosion, they do not split ortear, they do not separate from the core, they are practically free ofstresses, they do not scale but remain bright. The temper of the core isnot influenced. The exact, reliable and shake-free devices which shouldbe provided for adjusting and matching the other operating conditionsenable, e.g., the adjustment of any desired thickness of the hardenedlayer by a change of working conditions or the maintenance of a giventhickness of the hardened layer for longest periods with a fixedsetting. This enables full automation, particularly of the hardeningtreatment according to the invention. For instance, when it is desiredto form a particularly smooth surface, having a depth of roughness ofless than 0.1 on a small shaft, the workpiece is given a high speedrelative to the shaft (120 meters per second). As a result, the shaft inslight contact with the tool is given a speed of 2OG,OO0 rotations perminute. In this case the working pressure between the tool and workpieceamounts only to a few grams. On the other hand, these operatingconditions can be changed so as to cause a. plastic deformation of theworkpiece or to weld two workpieces together or perform other machiningor other treatments thereon.

The following results, described by way of example, have been obtainedwith experimental set-ups:

(1) A particularly simple experiment resides in moving a thincylindrical steel disc, rotating at a peripheral speed of 120 meters persecond, in the longitudinal direction, e.g., at mm./sec. over a gripped,pre-hardened steel strip, against which the disc is urged under lowpressure, e.g., of 50 grams. By this treatment the steel strip is groundto a very low depth of roughness, eg of 0.2/,u., and hardened. Thesurface of the resulting hardened layer is bright and resistant tocorrosion. Due to the moving small working area and the relatively largemass of the workpiece and the air entrained by the high-speed tool it isnot necessary to provide an additional coolant. Blued steel strip havinga carbon content of about 0.8% and a core having a micro-hardness of450-500 kg./ sq. mm., can be ground and finished in this way to attain asurface having a micro-hardness of 1100-1200 kg./sq. mm., measured undera load of 25 gram. The depth of grinding under a working pressure of 500grams is 0.1 mm., the thickness of the layer is 0.05 mm.

Blued Steel Strip, 0.6 mm. Thick Absolute speed of tool 120 meters/sec.Feed rate of tool 0. Pressure between tool and workpiece Approx. 20grams/sq. mm.

(2) Teeth produced in narrow, thin strip by reaming were given at thesame time a hardened layer 0.08 mm. thick. This layer was uniformlyformed on the cutting and rear faces and at the tip of the teeth. Thelayer is inseparably bonded to the rest of the material; it will notcrack or peel, is resistant to corrosion, has an extremely highresistance to corrosion and attains a micro-hardness of 1150-1250kg./sq. mm. under a load of 25 grams/sq. mm. The micro-hardness of therest of the material amounted to about 600-650 kg./ sq. mm. under thesame load. Such saws will readily cut hardened steel; the tips of theteeth will remain intact even after prolonged use.

Saw Blading Absolute speed of tool 120 meters per second. Feed rate oftool, three reversals- 9.2 cm./ sec. Pressure between tool and WorkpieceApprox. 500 grams. Absolute speed of workpiece.. Approx. 1.7 mm./ sec.Initial hardness of blading (micro-hairdness under a load of 25grams/sq. mm.) 700 kg./sq. mm. Carbon content 0.9%. Micro-hardness undera load of 25 grams/sq. mm. after the treatment 1100-1500 kg./ sq. mm.Thickness of hardened layer 0.05-0.1 mm.

(3) Using a parting tool which had been ground and hardened according tothe invention, 1350-1450 rings were cut from steel tubing whereas only950 rings, at most, could be cut trom the tubing with parting tools ofsteel tempered by ordinary methods.

6 Grinding a Parting Tool Absolute speed of tool 120 meters/ sec. Feedrate of tool 0. Pressure between tool and 'workpiece Approx. 5-10gra-ms/ sq. mm.

Absolute speed of workpiece 0. Initial hardness of workpiece(micro-hardness under a load of 25 grams/sq. mm.) 700 kg./sq. mm. Carboncontent 0.9%. Micro-hardness under a load of 25 grams/ sq. after thetreatment 1050 kg./sq. mm. Thickness of hardened layer 0.01-0.02 mm.

(4) A shaft is rotatably carried between centers. By means of the disc,this shaft is given a speed which is lower or higher than or equal tothe speed of 120 meters/ sec. of the disc. The thickness of theresulting hardened surface layer depends on the working pressure betweenthe tool and the workpiece. The depth of roughness does not exceed0.2,u.

Surface Treatment of Round Shaft, 5 mm. in Diameter Absolute speed oftool 120 meters/ sec. Feed rate of tool 0. Pressure between tool andworkpiece Slight pressure. Absolute speed of workpiece, driven by tool100,000 r.p.m. Initial hardness of workpiece (microhardness under a loadof 25 grams/ sq. mm.) 800 kg./sq. mm. Carbon content 0.9-1.1%.Micro-hardness under a load of 25 grams/sq. meter after the treatment1100 kg./ sq. mm. Thickness of hardened layer 0.01 mm.

(5) A steel disc having a working edge termed in accordance with thedesired profile of a screw thread and rotated at high speed is caused tocontact a bolt, which is axially fed and rotated at the same time. Thisresults in the formation of a screw thread, the sides of which areshaped, tempered and hardened at the same time.

*(6) Plastic deformation will result if the working pressure between thetool and the workpiece is substantially increased in Example 6.

(7) When two or more wires or metal sheets are contacted under anappropriate pressure by a disc which rotates, e.g., at 120 meters persecond and is moved, e.g., in the longitudinal direction of the wires orsheets, this will result in a very uniform and durable welded joint.

It is emphasized that all examples can be carried out with a simple toolrotating at high speed.

I claim:

A process for the treating of surfaces of hardened steel, especiallytools, for the purpose of hardening the surtace, comprising heating witha fast rotating steel disk having a peripheral speed beyond meters persecond to the hardening temperatures by :friction, then quenching by thedeeper located cool layers of the steel, said heating progressing overthe surface to or beyond the melting point with simultaneouslyquenching.

References Cited in the file of this patent UNITED STATES PATENTS974,099 Sundborg Oct. 25, 1910 1,799,614 Coberly Apr. 7, 1931 2,424,794Brown July 29, 1947 2,670,528 Brunberg Mar. 2, 1954 2,935,364 Smith May3, 1960

